Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

readOnlyHint=true already establishes this is a safe read, so the annotation bar is met. The description adds value by disclosing what each result contains (default fields plus custom fields), which matters because there is no output schema. It does not discuss pagination limits or ordering behavior, keeping it short of a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two tight sentences with the purpose and return shape front-loaded and no filler. The trailing 'OpenPhone REST: GET /contacts' is mostly noise for an agent choosing a tool, slightly diluting an otherwise efficient description.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description usefully summarizes the returned contact fields, and the parameter surface is fully covered by the schema. For a simple optional-filter list tool with readOnly annotations, this is nearly complete; only pagination/ordering behavior is left unaddressed.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents all four parameters including ranges and defaults. The description restates the externalIds and sources filters but adds no syntax or format detail beyond the schema, and says nothing about pageToken/maxResults — the expected baseline of 3.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('List contacts in the workspace') plus the filtering scope, which is enough to separate it from most siblings. It does not explicitly name openphone_get_contact as the single-contact alternative, so sibling differentiation is only implied by the List/get split.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage by stating the tool is for listing contacts with optional external-id/source filters, but it never states when to prefer this over openphone_get_contact or how it relates to the other list_* tools. No exclusions or prerequisites are given.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.